Fish-raising or "pisciculture" is being widely adopted as an effective way of providing healthful high-protein food of uniform kind and quality. In contrast, fish caught naturally vary greatly in age, size, and quality. Moreover, fishing at large is becoming increasingly expensive and less certain of success, in great part because of past over-fishing and environmental disturbance. Nor can such fishing meet the increasing demand for quantity, quality, and uniformity of product.
Conventional culturing of fish occurs in natural or man-made bodies of water under quasi-natural conditions, susceptible to predation and disease. Somewhat more controlled environments are represented by net-pens, within which fish are confined--but at a necessarily low concentration or density--and hatchery raceways, usually located near a spring or similar source from which water is diverted to flow through such raceways at intermediate speed conducive to somewhat higher fish concentrations or densities.
Maintaining loosely confined fish free of both infection and injury is very difficult. Moreover, although their uniformity is often better than in a conventional catch, such fish continue to compete vigorously for food, whereupon those that have an initial advantage become disproportionately larger, much as in the wild. Net pens, pools, and similar enclosures are well known in the art. Illustrative patents of that general type include U.S. Pat. No. 513,319 to Hoxsie; U.S. Pat. No. 2,944,513 to Keely; U.S. Pat. No. 3,166,043 to Castillo; U.S. Pat. No. 4,394,846 to Roels; Horrex Brit. Pat. No. 1,590,781; and also Nystrom international publication WO 85/08158 of PCT/SE84/00364.
Illustrative fish raceways are shown in U.S. Pat. No. 4,044,720 to Fast; U.S. Pat. No. 4,267,798 to Collins; and U.S. Pat. No. 4,516,528 to Jones, featuring (in the same order) floating and upwelling, geothermal heating, and aeration--each plus waste removal. Raceway processing conditions are disclosed by Ruane et al. in "Characterization and Treatment of Waste Discharged from High-Density Catfish Cultures", in Water Research, vol. 11, no. 9, Pergamon Press (1977), pp. 789-800.
Raceway designs are reported by Heard and Martin in "Floating Horizontal and Vertical Raceways Used in Freshwater and Estuarine Culture of Juvenile Salmon", etc., in Marine Fisheries Review issue of March 1979, pp. 18-23. Comparisons of net pen and raceway aerobics and fish conditions are made in exhaustive detail by Michel Besner in a 200-page 1980 Ph.D. dissertation (including 20 pp. of citations), University of Washington College of Fisheries, but his experimental results do not seem to have had an appreciable effect upon commercial fish culturing insofar as is known.
There is an increasing need for improving fish culture, and the present invention is directed to meeting that need, in part by extending existing procedures or trends, but also in part by going contrary to accepted principles and practices.